1. Field of the Invention
The present invention relates generally to air conditioning systems, and, more particularly, to an air distributing mechanism for air conditioning systems in automotive vehicles.
2. Description of the Related Art
Automotive air conditioning systems having a passenger compartment air temperature control device are known in the art. Generally, an automotive air conditioning system is provided with a heat exchanger which is fluidly connected to and driven by an engine, that radiates heat introduced to the heat exchanger by a flow of engine coolant. The automotive air conditioning system controls the heating of the passenger compartment. A coolant pump, which is also fluidly connected to the engine, circulates the coolant.
The temperature of the passenger compartment is controlled by either a manual control mechanism or by an automatic control mechanism which employs an algorithm to achieve a predetermined temperature. For example, U.S. Pat. No. 5,226,595 to Devera et al. (Unexamined Japanese Publication patent, No. H5-246230) are known.
FIG. 1 discloses an overall configuration of a known air conditioning system. An air conditioning system 100 includes duct unit 101 provided with a blower device 112; an inside air inlet opening 110, which communicates with the automobile compartment to exhaust recirculated air; and an outside air inlet opening 111, which communicates with an external space. These inlets are opened and closed by a damper 109. Air conditioning system 100 further includes evaporator 102, which is a part of a refrigerant circuit for cooling air passing therethrough; heater core 103 disposed downstream from evaporator 102; and a plurality of outlets (e.g., a defroster outlet 113 and a floor outlet 114), each of which opens into the automobile compartment.
Heater core 103 is fluidly connected to engine 104 and receives engine coolant from engine 104 through a coolant pump 105, vehicle radiator 108, and control valve mechanism 107, each of which is serially connected to engine 104 by a fluid passageway 106. Coolant pump 105 is driven by engine 104 via an engine driven member, such as a belt.
Further, an air temperature sensor 115 for detecting the temperature at the rear of heater core 103 is disposed downstream from heater core 103 and is electrically connected to an electric control unit 117 that controls the opening and closing of control valve 107. A temperature setting device 116 also is electrically connected to electrical control unit 117 to control a set temperature "TS."
In the operation of air conditioning system 100, coolant that is heated by engine 104 is pumped into heater core 103 by coolant pump 105 with control valve 107 regulating the amount of the flow of coolant therethrough. The coolant is cooled in radiator 108, as required, and is circulated within fluid passageway 106.
Air is drawn from inside and outside air inlet openings 110 and 111 by closing or opening damper 109, and flows into the automotive compartment from outlet openings 113 or 114 through evaporator 102 and through the coils of heater core 103. Typically, air circulation is forced by blower device 112.
Further, set temperature "TS" is determined according to temperature setting device 116 in a manual air conditioner. In an automatic air conditioning system, set temperature "TS" is determined in response to several factors, including temperature setting device 116, the temperature in the passenger compartment, the air temperature outside, and the quantity of solar radiation entering the vehicle.
The temperature of the air discharged to the passenger compartment is controlled by regulating the opening of control valve 107. Sensor 115 generates a sensor signal by detecting air temperature "TO" at outlet of heater core 103. Temperature setting device 116 generates a setting signal by determining set temperature "TS."
Sensor and setting signals are input continuously into electric control unit 117. Using these signals, electric control unit 117 computes a value for opening "FB" at control valve 107 that is necessary to achieve the desired vehicle compartment temperature "TS" using the automatic feed-back algorithm shown in FIG. 2. The terms "q" and "r" in arithmetic feedback algorithm represent coefficients.
Several factors may alter the operation of the air conditioning system. For example, a change in the rotation speed of engine 104 alters the amount of coolant that flows to the heat exchanger; a change in rotation speed of blower device 112 alters the air quantity generated by blower device 112; the mixture of interior air with exterior air exhausted from interior and exterior air outlet openings 110 or 111 alters air temperature at an inlet of evaporator 102; and, the activation or de-activation of a compressor (not shown) fluidly connected to evaporator 102; and the change in air temperature outside the vehicle alters air temperature at the inlet of evaporator 102. Therefore, in these conditions, the disturbances discussed above may cause a change in the outlet air temperature "TO" of heater core 103 blown from outlet openings 113 or 114 because outlet air temperature "TO" is controlled by only feedback control (PI control or PID control). Accordingly, this results in an uncomfortable environment for a vehicle passenger whenever outlet air temperature "TO" of heater core 103 increases.
In addition, if coefficients "q" and "r" in the arithmetic feedback algorithm are regulated to prevent a change in outlet air temperature "TO," control valve 107 exhibits a "hunting" phenomena and becomes unstable.
FIG. 3 illustrates the control characteristic curves of control valve 107. It shows that outlet air temperature "TO" of heater core 103 changes significantly in response to change 121 in inlet air temperature "TI," change 122 in rotation speed of engine 104, change 123 in voltage of blower 112, and change 124 in set temperature "TS." Further, the regulation of control valve 107 tends to be unstable, i.e., to overshoot the desired valve position or to exhibit a "hunting" condition. For instance, when the passenger in the vehicle changes set temperature "TS," it takes a significant period of time for the outlet air temperature "TO" to rise to meet set temperature "TS." It takes additional time for the air temperature in the passenger compartment to reach the set temperature "TS. "
These and other problems in the related art are addressed by the invention described below.